At a fair, 3 plates of nachos and 2 glasses of milkshake cost Rs 250, while 2 plates of nachos and 3 glasses of milkshake cost Rs 225. By how much (in Rs) does one plate of nachos cost more than one glass of milkshake?

Let a plate cost Rs $x$ and a glass Rs $y.3x+2y=250$ and $2x+3y=225$. Adding: $5x+5y=475$, so $x+y=95$. Subtracting: $x-y=25$. (Then $x=60$ and $y=35$; check 180 + 70 = 250 and 120 + 105 = 225.) 95 is what one of each costs together, which comes from adding instead of subtracting; 60 and 35 are the two prices themselves, not the difference asked for.